LONDON, England (AP) -- Authorities grounded three British Airways jetliners in London and Moscow on Wednesday and drew up plans to contact thousands of airplane passengers as they broadened their investigation into the radiation poisoning death of a former Russian spy.

Two planes at London's Heathrow Airport tested positive for traces of radiation, a third plane has been taken out of service in Moscow awaiting examination.

Home Secretary John Reid disclosed the search following a meeting with COBRA, the government's emergency committee. Reid said two planes had been tested so far and that another would be tested.

The initial results of the forensic tests had shown very low traces of a radioactive substance onboard two aircraft, British Airways said in a statement.

The company added that the investigation is confined to the three planes, which will remain out of service until further notice.

High doses of polonium-210 -- a rare radioactive element usually manufactured in specialized nuclear facilities -- were found in Alexander Litvinenko's body, and traces of radiation have been found at sites in London connected with the investigation of his death.

The airline said it was contacted by the British government late on Tuesday and told to ground the planes, and allow investigators looking into the death of the former intelligence agent to test them for radiation.

All three planes had been on the London-Moscow route, British Airways said. In the last three weeks the planes had also traveled to routes across Europe including Barcelona, Frankfurt and Athens. Around 30,000 passengers had traveled on 220 flights on those planes, said Kate Gay, a spokeswoman for the airline.

"The airline is in the process of making contact with customers who have traveled on flights operated by these aircraft, which operate within Europe," British Airways said in a statement, adding the risk to the public was low.

The airline has published the flights affected on its Web site, and told customers on these flights to contact a special help line set up by the Health Ministry.